This invention is generally directed to resin compositions useful for incorporation into toner and developer compositions. More specifically, the present invention relates to polysiloxane resins, especially polydialkylsiloxanes crosslinked styrene/butadiene and polydiarylsiloxanes crosslinked styrene/butadiene copolymers useful for the formulation of toner compositions that can be selected for imaging processes wherein silicone release oils are avoided or such oils are contained in the toner composition. In one embodiment, there are provided in accordance with the present invention polydialkylsiloxanes or polydiarylsiloxanes crosslinked styrene/butadiene copolymers resins that can be selected for the formulation of toner compositions containing pigment particles, and optional additive particles. In addition, the present invention is directed to rapid processes for the preparation of the aforementioned resins by suspension free radical polymerization processes and wherein products of high purity and high yields are obtained. Processes for the preparation of the aforementioned copolymers using free radical procedures can be accomplished generally by the emulsion polymerization techniques as illustrated in U.S. Pat. No. 4,469,770; and the suspension polymerization processes as illustrated in U.S. Pat. No. 4,558,108, the disclosures of each of these patents being totally incorporated herein by reference, providing that the appropriate reactants are selected and there results the copolymers of the present invention. The toner and developer compositions formulated with the polysiloxane resins illustrated herein are particularly useful in electrophotographic imaging methods with soft roll fusers, and wherein release agents, such as silicone oils, selected to prevent toner particles from adhering to the surface of the fuser are not needed, or are incorporated into the polysiloxane crosslinked resins illustrated herein. Furthermore, the aforementioned copolymers contain polysiloxane blocks that also function as crosslinks between the styrene and the butadiene. While it is known that divinylbenzene crosslinks may increase the durability and elasticity of resins, the polysiloxanes of the present invention, in addition to possessing the aforementioned functions, enhance toner release, that is since they are present as crosslinks or are functioning as crosslinking agents between styrene/butadiene copolymer chains, they enhance toner release by increasing the elasticity and durability of the resin.
There were located as a result of a patentability search (1) U.S. Pat. No. 4,340,660, which discloses toners with crosslinked vinyl polymers having a gel content of 50 to 99 percent and a crosslinked polymer having a gel content of 10 to 0 percent, reference for example the Abstract of the Disclosure; also note column 5 of this patent wherein a mixture of a styrene butadiene copolymer with a polysiloxane is disclosed; (2) U.S. Pat. No. 3,526,533, wherein carriers with, for example, copolymeric carrier coatings are disclosed and wherein the silicon prepolymers include those with ethylenic or acetylenic linkages, reference columns 4 and 5; (3) Japanese Patent Publication Abstract No. 62-108262, which discloses a toner formed with an acryloxy silane and styrene; and (4) as background interest U.S. Pat. Nos. 3,053,688; 3,054,751; 3,215,527; 4,039,331; 4,142,982 and 4,430,408. With further respect to U.S. Pat. No. 3,526,533, the terpolymer carrier coating materials are comprised of polymers that are random, block or graft (which are essentially branched polymers) copolymers. There is, however, no teaching in this patent of crosslinked materials, especially polysiloxane crosslinked materials, wherein the polysiloxane portion is not a block or a graft (branch) but instead is the crosslinking function joining two styrene/butadiene copolymers together. Also, the prepolymer polysiloxanes of this patent have only one free radical reactive function per chain (or a functionality of 2). In contrast, for example, with the polysiloxanes of the present invention two free radical functions on each chain are selected (or a functionality of 4), one on each end.
Also, toner and developer compositions, especially those containing charge enhancing additives, are well known, reference for example U.S. Pat. Nos. 3,893,935; 3,944,493; 4,007,293; 4,079,014 and 4,394,430. Thus, for example, there is described in U.S. Pat. No. 3,893,935 the use of certain quaternary ammonium salts as charge control agents for electrostatic toner compositions. Further, there are illustrated in U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference, developer and toner compositions having incorporated therein as charge enhancing additives organic sulfate and sulfonate substances. A similar teaching is present in U.S. Pat. No. 4,394,430, the disclosure of which is totally incorporated herein by reference. Moreover, there are disclosed in U.S. Pat. No. 4,298,672, the disclosure of which is totally incorproated herein by reference, positively charged toner compositions with resin particles, and pigment particles; and as a charge enhancing additive, alkyl pyridinium compounds, inclusive of cetyl pyridinium chloride.
Additionally, toner and developer compositions useful in xerographic imaging processes wherein silicone oils are not needed are known, reference for example U.S. Pat. No. 4,556,624, the disclosure of which is totally incorporated herein by reference. In this patent, there are disclosed, for example, improved positively charged toner compositions comprised of a polyblend mixture of crosslinked copolymer compositions, a second polymer, pigment particles, and a particular wax component thereby enabling the toner compositions to be selected for imaging systems wherein release fluids are not required. The types of resin described in this patent and other patents relating to toner compositions, including those compositions useful in imaging methods wherein release fluids are avoided, include polyamides, epoxies, diolefins, polyurethanes, vinyl resins and polymeric esterification products of a dicarboxylic acid, and a diol comprising a diphenol. Typical monomers selected for the preparation of the appropriate aforementioned resins include styrene, p-chlorostyrene, unsaturated mono-olefins such as ethylene, propylene, butylene, isobutylene and the like; vinyl esters such as esters of monocarboxylic acids including methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methylalpha-chloroacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, and other similar acrylates; acrylonitrile, methacrylonitrile, and acrylimide; vinyl ethers such as vinyl methyl ether, vinyl isobutyl ether, vinyl ethyl ether, and the like; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, and methyl isopropenyl ketone, and N-vinyl indole, N-vinyl pyrrolidene, and the like; styrene butadiene copolymers; and mixtures thereof.
As preferred toner resins illustrated in the '624 patent, there can be selected styrene polymers, and the esterification products of a dicarboxylic acid, and a diol comprising a diphenol. The aforementioned polyesters are illustrated in U.S. Pat. No. 3,590,000, the disclosure of which is totally incorporated herein by reference. Other specific preferred toner resins include styrene/methacrylate copolymers; styrene/butadiene copolymers; polyester resins obtained from the reaction of bisphenol A and propylene oxide, followed by the reaction of the resulting product with fumaric acid; branched polyester resins resulting from the reaction of dimethyl terephthalate, 1,3-butanediol, 1,2-propanediol, and pentaerythritol; styrene/butadiene copolymers prepared by a suspension polymerization process, reference U.S. Pat. No. 4,558,108, the disclosure of which is totally incorporated herein by reference; styrene/butadiene resins prepared by an emulsion polymerization process, reference U.S. Pat. No. 4,469,770, the disclosure of which is totally incorporated herein by reference; and Pliolites.
Furthermore, illustrated in U.S. Pat. No. 3,418,354 are processes for obtaining olefin-polyoxyalkylene copolymers by a graft reaction with a peroxide, whereby there are generated free radical sites on the backbone polymer. One process embodiment disclosed in the '354 patent involves the addition of an alpha olefin, such as styrene, and a peroxide to a polyoxyalkylene compound, such as a siloxane, wherein there results a graft copolymer; and more specifically, an olefin-polyoxyalkylene graft copolymer, see column 2, line 23. In Japanese Patent Publication No. 46-9355, there is disclosed a process for the preparation of graft block copolymers with a polysiloxane chain by the reaction of a functional polysiloxane with a polymer obtained from the anion polymerization of a styrene or a butadiene. Japanese Patent Publication No. 58-225103 discloses a method for the crosslinking of a thermoplastic resin by the reaction of a hydrogenated styrene-butadiene-styrene block copolymer with a silane in the presence of organic peroxides. Further, in U.S. Pat. No. 3,691,257 there are disclosed organic polymers modified by incorporating therein a siloxane polymer organic block copolymer; while Japanese Patent Publication No. 57-187345 describes a rubber modified styrene resin prepared by continuous bulk polymerizations in the presence of organic polysiloxanes and 1,2-vinyl polymers.
In U.S. Pat. No. 4,770,968, the disclosure of which is totally incorporated herein by reference, there are illustrated toner and developer compositions with branched polysiloxane styrene/butadiene terpolymers of the formula, for example, as recited in claim 1. These branched copolymers differ from the copolymers of the present invention in that, for example, each polysiloxane unit is part of only a single styrene/butadiene copolymer as compared to the present copolymers in which each siloxane unit is attached to two styrene/butadiene copolymers. Accordingly, with the polymers of the present invention the topology is markedly different as these polymers possess, for example, a structure in which two styrene/butadiene copolymers are joined by a polysiloxane crosslink. In addition, physical properties associated with flow, such as melt index, are different with the resins of the present invention which possess less flow for a given size siloxane incorporated in a given amount (for example, 10 percent incorporation of a 5,000 molecular weight polydimethylsiloxane provides a melt index of 12 grams/10 minute for a resin of the present invention but provides a melt index of 9.3 grams/10 minute for a corresponding branched polydimethylsiloxane resin).
Furthermore, there are illustrated in U.S. Pat. No. 4,894,309, the disclosure of which is totally incorporated herein by reference, processes for the preparation of crosslinked polymers wherein, for example, divinylbenzene is selected as the crosslinking component. More specifically, the patent discloses a free radical suspension polymerization process for obtaining crosslinked styrene butadiene ternary copolymers, which comprises the polymerization of styrene monomers, butadiene monomers, and crosslinking components in the presence of a surfactant, a stabilizer, and a first and second initiator; and wherein the aforementioned components are present in an aqueous phase; heating the resulting aqueous mixture at a temperature of from about 50.degree. C. to about 110.degree. C.; thereafter heating the mixture at a temperature of from about 110.degree. C. to about 150.degree. C.; followed by cooling; and isolating the desired product.
There is a need for new toner resins that possess desirable characteristics, and that are useful in electrophotographic imaging systems wherein, for example, release oils are avoided. Additionally, there is a need for simple economical processes that enable the preparation of crosslinked polysiloxane resins in high yields exceeding 80 percent, for example, and wherein the resulting products are of an acceptable purity exceeding in some instances 90 percent. There is also a need for novel toner resins which are useful as toner compositions when selected for the development of images, and wherein fixing is accomplished without the need for release fluids. In addition, there is a need for crosslinked resins useful for the formulation of toner compositions that possess desirable mechanical properties, excellent fusing characteristics, and acceptable release properties. Moreover, there is a need for developer compositions containing toner components, including the crosslinked polysiloxanes illustrated herein, and carrier components. There is also a need for imaging and printing methods wherein there are selected toner and developer compositions containing therein the crosslinked polysiloxanes disclosed herein, and wherein release fluids, such as silicone oils, are avoided during the fusing process. Moreover, there remains a need for improved toner compositions that are compatible with fusing rolls incorporated into imaging apparatuses, especially Viton fuser rolls. One main advantage of the polysiloxane crosslinked resins of the present invention is that they combine the properties of good release with increased elasticity and durability. This is usually not the situation with the prior art branched polysiloxanes, wherein a second resin, divinylbenzene crosslinked styrene/butadiene, is added to the toner formulation to increase elasticity and durability. Additionally, the aforementioned prior art materials can be regarded as block copolymers where the styrene/butadiene is one block and the polysiloxane a second block as contrasted to the present invention wherein, for example, the polysiloxane is a crosslinking agent joining at least two (or more) styrene/butadiene polymers.
With further respect to the invention of the present application, particularly the developer compositions thereof, one Viton soft fuser roll selected for use in electrophotographic copying machines is comprised of a soft roll fabricated from lead oxide and DuPont Viton E-430 resin, a vinylidene fluoride hexafluoropropylene copolymer. This roll contains approximately 15 parts of lead oxide and 100 parts of Viton E-430, which mixture is blended and cured on the roll substrate at elevated temperatures. Apparently, the function of the lead oxide is to control the generation of unsaturation by dehydrofluorination which can cause crosslinking, and to provide release mechanisms for the toner composition.